Method of producing fibrous glass



Sept. 10, 1946. A. SIMISON ETAL METHOD OF PRODUCING FIBROUS GLASSOriginal Filed March 26, 1942' 2 Sheets-Sheet 1 All 1; .5" E F lmls n""pz Fletcher ATTORNEY p 10, 1946 A; SIMISON ETAL METHOD OF PROISUCINGFIBROUS GLASS Original Filed March 26, 1942 2 Sheets-Sheet 2 MfL mvs7MPRA TURE INVENTORS .13- Simiaon u Ed Fletcher Allen VW ATTORNEY;

.lution of the ingredients of the Patented Sept. 10, 1946 2,407,456{METHOD OF PRODUCING FIBROUS GLASS Allen L. Simison and assignors toOwens-Cor Ed Fletcher, Newark, Ohio,

ning Fiberglas Corporation, Toledo, Ohio, a corporation of DelawareOriginal application March 436,236. Divided and this 26, 1942, SerialNo. application October 2, 1943, Serial No. 504,800

Claims.

This invention relates to the manufacture of glass filaments and moreparticularly to an improved method of feeding molten glass or similarheat-plasticized material in the attenuation of filaments.

The present application is a division of our copending applicationSerial No. 436,236, filed March 26, 1942.

In the production of glass filaments by attenuating a stream of moltenglass flowing through a small orifice in a. molten glass container, itis desirable to have accurate control of the temperature of the glass inthe region of attenuation. This is true whether the attenuation iseffected mechanically, for instance, by employing a rotating drum toattenuate the filaments and on which the filaments are wound, or whetherthe streams are attenuated by tractively engaging them with a gaseousblast moving in the direction of stream flow; Attenuation of glassfilaments by mechanical means in the form of a winding drum is describedin the United States Slayter and Thomas Patent No. 2,234,986 of March18, 1941, and by mechanical means in the form of coaoting gear-shapedrotors in the United States Slayter Patent No. 2,230,272 of February 4,1941. The Slayter and Thomas Patent No. 2,133,236 of October 11, 1938,describes the process of attenuating glass filaments or fibers by agaseous blast.

In order to rapidly produce fine fibers of regulable uniform diameter,the temperature of the glass should be accurately controlled during itspassage from the supply body to the point where the fibers may be saidto be completely formed. If attenuation takes place at too low atemperature the fibers are coarse and uneven .on their surfaces. Theresistance at low temperature requires greater pulling force andconsequently the consumption of more power, and resulting, in the caseof attenuation by means of a drum, in such tight packing of the strandson the drum as to interfere with their later removal. On the other hand,glass at too high a temperature is so watery and fiuid as to precludeattenuation. Constant temperatures are also necessary to obtainuniformity of the product.

The supply body of glass is preferably maintained at a temperaturehigher than the desired attenuating temperature to facilitate completeso-- nate all striae, cords and orientations of ingredients. For manyglass batches the desired at tenuating temperature is relatively nearand either above or below the devitrification point of the glass.Holding the entire supply body at the to attenuation of glass glass andelimiattenuating temperature or cooling it slowly from a highertemperature to the attenuating temperature entails the danger ofdevitrification. If, however," the supply body is held at a temperaturewell above the devitrification temperature and then at the orificereduced quickly to the attenuating temperature, devitrification isprevented.

It is an object of the present invention .to provide a method forobtaining accurate temperature control of the molten glass in theattenuating zone and to assure rapid reduction of the temperature of theglass in the neighborhood of this zone to the desired attenuatingtemperature. It is an ancillary object to cause the temperature of theglass in the region of attenuation to be dependent mainly upon thetemperature of the supply body and upon stable fixed factors and notupon applied cooling means, thereby permitting regulation of theviscosity of the glass-bein attenuated merely by regulating thetemperature of the supply body.

It is a further object of the invention to cause the reduction intemperature at a point close to the point of attenuation. The rapidreduction of temperature in the neighborhood of attenuation permitsholding only a minimum quantity of glass at the attenuating temperature,thereby eliminating the danger of incipient devitrification.

It is highly desirable in the interest of greater and more economicalproduction to maintain the viscosity of the glass being attenuatedsufiicient- 1y low so that only a minimum tension is required toattenuate each filament. However, in the case where the molten glassflows from metalwalled orifices, the glass at this low viscosity wetsthe metal and flows over the outside wall of the bushing, flooding theorifice and interrupting attenuation therefrom. The molten glasseventual- ,ly spreads to adjoining orifices and floods them in turn sothat within a short time the operation must be halted and the bushingcleaned. If the metal about the orifice is maintained sufiiciently coolto prevent flooding, it has been discovered that in prior bushings theglass flowing through the orifice passage was of such a high viscositythat the attenuating force necessary was unduly increased.

It is a further object of the present invention to obtain both of theabove desired properties simultaneously. The glass being attenuated isof sufficiently low viscosity to permit attenuation with a minimumattenuating force and the metal surrounding the orifice is sufficientlycool to prevent wetting thereof by the molten glass, thereby eliminatingflooding.

It, is also an object of the present invention to reduce the resistanceto flow of the molten glass through the orifice passage as its viscosityincreases to the desired attenuating viscosity so that the glass may becooled suiliciently to be properly attenuated and to prevent flooding ofthe orifice without unduly increasing the resistance to movement of theglass through the orifice passage. More particularly, it is an object toreduce the rate of flow of the molten glass as its viscosity increases.Since the viscous resistance of a, liquid is directly proportional tothe rateiof movement thereof, a reduction in the rate of flow of themolten glass lessens the eflect of increased viscosity.

It is a still further object of the invention to provide a glass feedingorifice from which the glass will flow under the action of gravity whenattenuation is interrupted although the orifice is of small size and theviscosity of the glass is sufiiciently high to prevent wetting of theouter metal walls of the orifice. This provides for automatic startingof stream flow.

Other objects, as well as advantages. of the present invention will beapparent from the following description. In the drawings:

Figure 1 is a schematic elevational view of apparatus for the productionof continuous filaments by mechanical attenuation; Figure 2 is aschematic elevain'onal view of apparatus for attenuating the filamentsby means of a gaseous blast;

Figure 3 is a, longitudinal vertical section of the bushing of thepresent invention on a greatly enlarged scale and partly broken away;

Figure 4 is a sectional view on a like scale of a bushing tipillustrating a modified form; and

Figures .5 and 6 are similar views illustrating further modifications.

The present invention provides a bushing for feeding small streams ofmolten glass and havwith a straight portion ing passages therein throughwhich the glass flows, so constructed as to eliminate the (hillcultiesencountered heretofore. More particularly the bushing is provided withtips or nipples ing Iii is provided for feeding molten glass in amultiplicity of small streams from its bottom wall. Glass already moltenmay be fed into the upper end of the bushing, or cullet or raw batch maybe fed thereinto and melted in the bushing.

The bushing is formed'of a heat resistant precious metal or preciousmetal alloy and is heated by passing an electric current through itswalls.

The small streams of molten glass flowing through openings in the bottomof the bushing may be attenuated into filaments by means of i 2 uponwhich the filaments are wound to form a package. Intermediate the drumand the bushing the filaments pass over a pad 13 which is arranged togroup the filaments into a strand and to apply a, suitable lubricant or'sizing to the filaments. The pad may be of any suitable type such, forinstance, as that shown and described in the Fisher Patent No.2,224,149.

glass fibers by means of a gaseous blast. This apparatus may include abushing 20 similar to the bushing Ill arid heated in like manner.

Spaced beneath the bottom of the bushing 20 is a blower 2| provided withoppositely disposed The Slayter and Thomas Patent No. 2,133,236 morefully discloses this method of producing glass fibers. The fibers, afterthey are formed. may be deposited on a moving foraminous surface 24spaced 9, suitable distance beneath the blower.

The bushings i0 and 20 are each provided on their bottom wall 25 with aplurality of nipples or tips 28 projecting outwardly a substantialdistance therefrom. The tips constitute a preliminary cooling zonethrough which the glass passes before reaching the region of attenuationas will be brought out in detail as the description progresses. Each ofthe tips has a passage 21 extending therethrough communicating at itsinner end with the interior of the bushing and opening to the atmosphereat its outer end 28. The inner end of the passage 21 is preferablygradually converging in cross-section as shown at 29 so that the moltenglass is inducted in a smooth streamline flow into the passage. Theconverging portion of the passage directly communicates 30 which in turnis in communication with a straight sided enlarged passage 3|. At itspoint of meeting with the passage 36, the passage 3i is preferablyrounded as at 32 to permit the glass to flow into the larger passagewithout the formation of eddy currents and to eliminate any pocketswhere the glass may be quiescent.

The walls surrounding each passage 21 preferably gradually decrease inthickness from the bottom 25 of the bushing to the point where thepassages 30 and 3i join. At this point the wall is abruptly reduced inthickness and then again gradually decreases in thickness from therounded portion 32 to the outer end 28 of the tip.

This tapering cross-section of the wall facilithe molten glass flowingso that it flows through said passage at a viscosity lower than theattenuating viscosity. As the molten-glass flows into the enlargedpassage 3!, its rate of cooling is accelerated because of the fact thathere the wall of the tip is abruptly reduced in thickness and alsobecause the enlarged passage 3! slows down the rate of flow of themolten glass to increase the rate of cooling. As the molten glasscontinues its movement through the passage 3! it continues to cool atthe increased rate so that by the'time it reaches the lower end of thetip it is at the desired attenuating temperature and proper viscosity.The rate of cooling of the glass as it moves through the passage 3| isgreater than the rate of cooling in the l V passage 30 so that the glassis rapidly cooled in the neighborhood or the devitriflcation point tominimize the danger oi! devltriflcation.

The enlarged passage 3| serves a further purpose in that the body ofmolten glass therein constitutes a reservoir of molten material so thatupon slight momentary fluctuations in operating conditions, theattenuation will not be disrupted. Thus, an instantaneous chilling oithe tip will not aflect the relatively larger body of glass in thepassage 3| sufllciently to stop attenuation. Also, localized bodies ofglass at higher temperatures flowing into the larger passage 3| will be,

' to a large extent, equalized.

Although, the manner in which the tip of the present invention acts tominimize the attenuating force required and at the same time preventflooding of the bushing tips is not completely understood, it may bethat the enlarged passage 3| permits a differential in temperaturebetween the central portion of the, molten glass in the pas:-

, sage 3| and the outer portion or such glass adjacent the wall of thepassage. Thus the glass toward the center is of a sufllciently lowviscosity to require only a minimum of tension to attenuate it while theglass adjacent the wall of the passage and the metal of the wall areatsufliciently low temperatures to prevent the glass from wetting themetal and flooding the tip. A straight passages does not provide thesame results, which may be due to the fact that a straight passage ofsuflicient diameter to provide the required temperature gradienttransverse to the direction of flow of glass permits too great a flow ofglass, so that regulation of attenuation is difficult and the increasedquantities of glass tend to flood the orifice. If the glass in astraight passage is maintained at a temperature sufliciently low toreduce the flow, then it is iound that the required attenuating force isunduly increased. In the present case, the narrow passage 30 controlsthe rate of flow of the molten glass while at a high temperature and theincrease in viscosity of the glass to attenuating viscosity takes placein the enlarged passage 3 I The present invention realizes both aminimum attenuating force and a complete freedom from flooding.

It has been discovered that for a given temperature the filamentsattenuated from the molten glass flowing through the tips vary in sizewith the rate of attenuation. At normal operating temperatures therelation of speed of attenuation to the size of filament attenuated issuch that the quantity of glass pulled always remains substantially thesame This does not always hold true at lower temperatures wheresometimes increase in the pulling rate may actually cause an increase inthe amount of glass pulled and result in coarser fibers; However, athigher temperatures, the higher the rate of pull, the smaller is theresulting filament.

We have found that because of this the passage 30 in the tip, whichcontrols to large extent the 6 oi flow of molten glass into the passage3! with a consequent greater amount of glass going into the filament.

The length of the passage 30 also governs the rate oi flow of the moltenglass and it must be proportioned to obtain the proper rate of flow,

variations in its length perceptibly affecting the rate or flow of theviscous glass therethro gh. The enlarged passage M is of a diameter andlength so proportioned as to provide the desired temperature drop of themolten glass flowing therethrough and to hold a proper quantity ofmolten glass.

With bushing orifice passages heretofore employed cessation ofattenuation of the stream flowing from the orifice causedthe glasstherein to stop flowing, apparently because the glass at the lower endof the orifice was quickly cooled by the metal walls when it ceased tobe drawn passage 23| merge into eachother more gradrate of flow ofmolten glass through the tip, may,

if desired, be of the same sizev regardless of the size of filamentbeing attenuated within reasonable limits and the desired regulations offilament size may be effected solely by varying the speed ofattenuation. However, to prevent going to inefficient very low speeds,it is desirable to increase the diameter of the passage 30 for theproduction of larger size filaments. The size of the passage 3| mayremain substantially he same, the only difference in operation beingthat the slightly larger passage 30 permits a higher rate out by theattenuating force. The glass at the end of the orifice was thus too cooland viscous to drop from the orifice under the action ofgravity.Operation could be started again only by initiating flow from eachorifice by means of a pick. This was a. time-consuming operation andgreatly reduced the efficiency of the operation.

The orifice passage of the present invention overcomes this difficultyby causing automatic starting of the flow of molten glass uponinterruption of attenuation. As the stream flows from the orifice itneed only be directed to the attenuating means and the operationresumed. This effect of the present orifice passage is believed due tothe fact that the lower passage of increased diameter results in ahigher temperature gradient of the molten glass lengthwise of thepassage. Upon interruption of attenuation and cooling of the moltenglass at the lower end of the passage, flow ceases, but the heat of theglass in the narrow passage directly above the enlarged passage isquickly communicated to the glass at the lower end of the orificepassage and flow of the glass is automatically resumed. I

The modified form of the invention shown in Figure 4 illustratesa'bushing bottom wall I25 provided with a tip I26 and having a passageI30 ending in an enlarged passage l3l at its lower end of frusto-conicalform, the lower end of said passage forming a sharp edge I50 with theouter wall of .the tip. This modified form of passage operates in amanner similar to the preferred form of the invention to accuratelycontrol the temperature and viscosity of the molten glass including thebushing wall and tip designated respectively by the numerals 225 and226, except that the passage 229, the passage 23!] and the ually and theentire passage in the tip has a smoothly curved interior wall.

Figure 6 illustrates a modification operative to obtain the moreimportant objects of the present invention and which lends itself tobeing formed by a simple die operation. In this form the bottom wal1 325of the bushing is provided with a tip 326 which may be formed first withstraight sides and then a wedge forced into the outer end of the tip toflare the walls of the tip and provide the illustrated diverging contourof the passage 321.

The present invention has the advantage that directed toward andimpinging upon the tips,

Because of this, the tips may be more closely spaced and the bushing maybe provided with many more orifices in any desired grouping orarrangement.

Various modifications may be resorted to within the spirit and scope ofthe appendedclaims.

We claim:

1. In the method of producing glass fibers by attenuating a stream ofmolten glass, the steps of establishing a supply body of molten glass ata temperature above the attenuating temperature and above thedevitrification temperature, flowing a stream of molten glass from saidbody, accelerating the velocity of the stream through a first coolingzone, and then rapidly cooling said stream to a temperature below thedevitrification point of the glass and decreasing the flow of the streamas it approaches the region of attenuation.

2. In the method of producing glass fibers by attenuating a stream ofmolten glass, the steps of establishing a supply body of molten glass ata temperature above the attenuating temperature, flowing a stream ofmolten glass from said body, accelerating the velocity of the streamthrough a first cooling zone, accelerating the rate of cooling of saidstream, b decreasing the velocity of the stream through a second zone,and increasing the rate of cooling over that in the said first coolingzone,

3. in the method of producing glass fibers by attenuating a stream ofmolten glass, the steps of establishing a supply body of molten glass ata temperature above the attenuating temperature of the glass, flowing astream of molten glass from said body, accelerating the velocity of thestream through a first cooling zone, then decreasing the velocity of thestream as it approaches the region of attenuation, and as said streammoves at decreased velocity cooling said stream at a higher rate ofcooling than in said first cooling zone.

4. In the method of producing glass fibers by attenuating a stream ofmolten glass, the steps 01. establishing a. supply body oi! molten glassat a temperature above the attenuating temperature, flowing a stream ofmolten glass from said body to the atmosphere and gradually cooling thestream as it moves away from said body, reducing the velocity of thestream as it approaches the atmosphere, and increasing the rate ofcooling of the-stream moving at said reduced velocity.

5. In the method of producing glass fibers by attenuating a stream ofmolten glass, the steps of establishing a supply body of molten glass ata temperature above the attenuating temperature and above thedevitrificaticn temperature of the glass, flowing a stream of moltenglass from said body to an attenuating region and gradually cooling thestream as it moves away from said body, reducing the velocity of thestream as it approaches the attenuating region, anddncreasing the rateof cooiing of the stream to bring it rapidly to a temperature below thedevitriflcation temper.

ature.

sum 11. fiilifiSON. m Ell-ETC

